Tungsten containing alloy

ABSTRACT

A HIGH TEMPERATURE ALLOY CONTAINING NICKEL AND, IN PERCENT BY WEIGHT, ABOUT 5.5% ALUMINUM, ABOUT 0.02% BORON, ABOUT 0.18% CARBON, ABOUT 10% COBALT, ABOUT 9.5% CHROMIUM, ABOUT 1.5% HAFNIUM, ABOUT 2.5% MOLYBDEUM, ABOUT 4.0% TITANIUM, ABOUT 1% VANADIUM, ABOUT 3.7% TUNGSEN AND ABOUT 0.06% ZIRCONIUM.

Sept. 18, 1973 HOCKIN ETAL.

TUNGSTEN CONTAINING ALLOY Filed Jan. 14, 1971 INVENTORS JOHN HOCKIN United States Patent 3,759,707 TUNGSTEN CONTAINING ALLOY John Hockin and Carl H. Lund, Arlington Heights, and

Wilbert P. Danesi, Deerfield, Ill., assignors to Martin Marietta Corporation, New York, N.Y.

Filed Jan. 14, 1971, Ser. No. 106,444 Int. Cl. C22c 19/00 US. Cl. 75171 6 Claims ABSTRACT OF THE DISCLOSURE A high temperature alloy containing nickel and, in percent by weight, about 5.5% aluminum, about 0.02% boron, about 0.18% carbon, about 10% cobalt, about 9.5% chromium, about 1.5% hafnium, about 2.5% molybdenum, about 4.0% titanium, about 1% vanadium, about 3.7% tungsten and about 0.06% zirconium.

HISTORY OF THE ART AND PROBLEM In U.S. application Ser. No. 725,074, filed Apr. 29, 1968, now abandoned it was disclosed broadly that inclusion of hafnium in cast, nickel-base alloys improved the ductility of such alloys at intermediate temperatures of about 1400 F. (760 C.). The present invention is concerned with a particular type of nickel-base casting alloy which is similar to Alloy E disclosed in said US. application Ser. No. 725,074, filed Apr. 28, 1968, now abandoned and has as its object the provision of highly improved alloys and castings made of said alloys suitable for use in gas turbines and other areas of utility involving exposure to high stress at a range of high temperatures.

It is an object of the present invention to provide novel highly improved alloys.

It is another object of the present invention to provide highly improved castings made of the novel alloy.

Other objects and advantages will become apparent from the following description taken in conjunction with FIG. 1 and FIG. 2 of the drawing which shows the microstructure of the highly improved alloys of the present invention.

DESCRIPTION Generally speaking, the present invention contemplates nickel-base alloys containing alloying elements in ranges of percent by weight as set forth in Table I.

1 Balance E.

With respect to the broad range, it is advantageous to balance the alloy composition with respect to the elements tungsten and titanium such that when the titanium is at the low end of the range, the tungsten is at the high end and vice versa. Those skilled in the art will appreciate that between these extremes any number of alloys can be formulated within the ambit of the invention. As a practical working guide one can be assured of obtaining excellent alloys within the ranges of the present invention it the sum of the percent titanium plus one-tenth the percent of tungsten is about 3.8% to about 4.5%.

"ice

The alloys of the present invention are advantageously made up using as pure materials as are commercially feasible. The nickel content set forth in Table I as Balance E is essentially the balance of the alloy and includes small amounts of impurities and incidental elements which do not detrimentally affect the basic and novel characteristics of the alloy. Those skilled in the art will appreciate that metals such' as lead, bismuth and the like, metalloids such as arsenic and non-metals such as phosphorus, sulfur, oxygen and the like are highly detrimental to nickel-base alloys of the kind disclosed herein and should be rigidly excluded.

It is highly advantageous to melt and cast the alloys of the invention under high vacuum and to employ current state of the art techniques of investment casting to provide cast hardware such as turbine blades for gas turbine engines. When cast in such a manner, the alloys of the present invention exhibit a microstructure which is substantially different from the microstructure of Alloy E of 11.8. application Ser. No. 725,074, filed Apr. 29, 1968, now abandoned as modified with hafnium. Alloy E modified with hafnium contains, in percent by weight, about 0.18% carbon, about 10% chromium, about 15% cobalt, about 3% molybdenum, about 4.7% titanium, about 5.5% aluminum, about 0.014% boron, about 0.06% zirconium, about 1.0% vanadium, about 1.5% hafnium with the balance being essentially nickel. The microstructure of both alloys show a basic gamma matrix having gamma-prime phase and carbides dispersed therethrough. The microstructures diifer in that in modified Alloy E the gamma-prime phase appears as cubic particles whereas in the alloy of the invention particles of this phase tend to be elongated. In the microstructure of modified Alloy E there are discrete islands of eutectic gamma-prime phase. With the alloy of the invention islands of eutectic gammaprime phase are non-discrete and tend to blend in with the matrix. Again, with modified Alloy E, discrete grain boundaries can be distinguished Whereas with the alloy of the invention grain boundaries can hardly be distinguished. The drawing shows the microstructure of the alloy of the invention as brought out by etching with a reagent made up by mixing 30 ml. of glycerol, 8 ml. of concentrated nitric acid and 6 ml. of 48% hydrofluoric acid. The drawing, showing magnifications of 250x in FIG. 2 and 1000 in FIG. 1, illustrates the points of difierence mentioned. It is to be noted that the microstructure as depicted in the drawing is associated with a reduction in titanium content from the level of modified Alloy E and that, when this microstructure is obtained by the least reduction of titanium content necessary to produce it along with inclusion of an efiective amount of tungsten, there are obtained cast alloys having an optimum combination of mechanical characteristics of engineering significance.

Levels of mechanical characteristics obtainable in alloys of the present invention are exemplified in the tables following'Table II. The compositions of specific alloys within and without the ambit of the invention are set forth (in percent by weight) in Table II.

Each of the foregoing examples and alloys were melted and cast under vacuum to provide cast-to-size, 0.250 inch. (6.35 mm.) test bars. These test bars were subjected to room temperature tensile tests and creep-rupture tests at 1800 (982 C.) and 1400 F. (760 C.). These tests show that the alloys of the present invention, i.e. Examples 1 and 2, exhibit highly advantageous mechanical characteristics when compared to characteristics exhibited by alloys outside the present invention. The results of room temperature tensile tests on cast-to-size specimens are set forth in Table III.

TABLE III Ultimate tensile 0.2% yield strength strength Red. in

Kg./ Kg. Elong. area,

Alloy K.s.l. mm. K.s.1. mm. percent percent Ex. 1 144.4 101. 7 120.4 84. 6. 5 9. 9 EX. 2 147. 103. 4 118. 9 83. 6 6. 5 9. 6 Alloy Y 148. 4 104. 4 116. 7 82. 0 9. 0 11. 7 Alloy Z 149. 2 105. 0 119. 5 83. 9 8.0 10. 4

Table III shows that at room temperature all four specific alloys tested exhibited substantially equivalent mechanical characteristics.

Creep-rupture data are set forth in Table IV.

Table IV shows that an alloy (Alloy Z) containing hafnium but with a low titanium content, that is an alloy wherein the percent titanium plus 0.1 times the percent tungsten is about 3.6, exhibits a relatively low life-to-rupture at 1800 F. as does Alloy Y which does not contain hafnium. At 1400 F. the alloy without hafnium (Alloy Y) has low prior creep and low life-to-rupture whereas the most advantageous alloy of the present invention (Example 1) has an extraordinarily long life-to-rupture and an excellent level of prior creep. Example 2 is an example of an alloy of the present invention which exhibits slightly higher life-to-rupture at 1800 F. than Example 1 at some sacrifice of 1400 F. characteristics.

Alloys of the present invention are particularly adapted to be used in the cast condition as gas turbine components and other structures which are subjected in use to stress over a range of operating temperatures. Another alloy of the persent invention containing in percent by weight 5.5% aluminum, 3.75% titanium, 2% molybdenum, 15% cobalt, 10% chromium, 0.014% boron, 0.06% zirconium, 0.18% carbon, 1% vanadium, 1.5% hafnium, 2% tungsten with the balance being nickel was melted and cast under vacuum into turbine blade molds. Specimens machined from the cast turbine blade gave room temperature tensile results of 127.0 k.s.i. ultimate tensile strength, 107.9 k.s.i. 0.2% yield strength, 8.5% elongation and 18.7% reduction in area. At 1400 1?. under a load of 85 k.s.i. specimens of the alloy machined from blades had lives of 206 and 226 hours, 2.85% and 3.56% prior creep, 3.2% and 3.8% elongation and 7.3% and 9.0% reduction in area. At 1600 F. under a load of 45 k.s.i. similar specimens had lives of 496.8 and 455.2 hours, 9.5% and 5.7% prior creep, 10.3% and 5.9% elongation and 15% and 13% reduction in area. These data show that metal taken directly from turbine blades cast of an alloy of the present invention is eminently suited for the intended use in gas turbines.

While the present invention has been described in conjunction with advantageous embodiments, those skilled in the art will recognize that modifications and variations may be resorted to without departing from the spirit and scope of the invention. Such modifications and variations are considered to be within the purview and scope of the invention.

We claim:

1. A cast alloy consisting essentially in percent by weight of about 4.7% to about 6.2% aluminum, about 0.002% to about 0.05% boron, about 0.10% to about 0.25% carbon, about 5% to about 20% cobalt, about 8.5% to about 12% chromium, about 0.8% to about 3% hafnium, about 1.5% to about 4% molybdenum, about 3.5% to about 4.5% titanium, up to about 1.5 vanadium, about 1% to about 4.7% tungsten, up to about 0.25% zirconium with the balance being essentially nickel, said alloy being balanced so that the sum of the percent titanium plus one-tenth the percent of tungsten is about 3.8% to about 4.5%.

2. A cast alloy as in claim 1 which contains 4.8% to 5.5% aluminum, 0.002% to 0.03% boron, 0.015% to 0.20% carbon, 7.5% to 12.5% cobalt, 8.5% to 11% chromium, 1% to 2% hafnium, 1.75% to 3.25% molybdenum, 3.5% to 4.2% titanium, 0.75% to 1.25% vanadium, 2% to 4.6% tungsten and 0.01% to 0.15% zircomum.

3. A vacuum-cast turbine blade made of the alloy of claim 1.

4. A vacuum-cast turbine blade made of the alloy of claim 2.

5. A cast alloy as in claim 1 containing about 3.7% tungsten and about 3.7% to about 4.2% titanium.

6. A cast alloy as in claim 1 containing about 2% tungsten and about 3.8% titanium.

References (Zited UNITED STATES PATENTS 3,479,157 11/1969 Richards et a1. --171 3,615,377 10/1971 Quigg et al 75171 RICHARD O. DEAN, Primary Examiner US. Cl. X.R. 148-325 

